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Re: RF and FODtrack-repair parts

Richard Lawn wrote:
> Cliff,
> Once again you've provided great assistance. I wish I still lived in Austin,
> TX where I had not only great access to Ham Sat elmers like Ron Parsons
> (W5RKN) but also easy access to buying parts. Oddly this is not the case in
> the Philly area where I now live. That bring me to ask you for suggestions
> on where to get parts mail order. I actually borrowed a FODtrack box from an
> Austin friend. We built 2 together and mine in not functioning. I think that
> when a problem (probably some stray current from lightning) attacked my
> Yaesu rotor control box and the rotor itself it also probably took out a
> chip or two in my FOD box. I've of course rebuilt my rotor and control box
> replacing a couple of pots but would also like to replace all of the chips
> in my FOD box and return my friends. Once again I'll have to find a parts
> source. Nothing is ever easy, but always rewarding when one solves the
> problems. 
> I'll be happy to document some of the problems and solutions that I've had
> for those who might be interested and once I get them all fixed.
> TNX AGN for your help
> 73
> Rick W2JAZ
> Richard J. Lawn, Dean
> College of Performing Arts
> The University of the Arts
> 320 S. Broad St.
> Philadelphia, PA 19102
> (215) 717-6125
> (215) 717-6128 FAX
> On 8/30/05 12:12 AM, "Cliff Buttschardt" <k7rr@arrl.net> wrote:
>>Lawn, Richard wrote:
>>>Anyone experience any problems with ARF getting into the FODtrack
>>   box and creating some havoc? Any solutions? System seems to be
>>   working well now with FOD and SatPC32, aside from the RF problems.
>>Hi John.  Yes, I had some difficulty with the FodTrack when I first
>>put into service.  The problem was RF getting into the box down the
>>rotor lines.  Put ferrite beads on all the rotor connections but
>>especially pins 3,4,5 and 6.  In addition, put a tiny capacitor say
>>220 pf to 1000 pf on these lines directly on the trace side of the
>>board.  There is plenty of room as a ground trace surrounds the board.
>>      Another modification was to put 0.1 ufd caps from pin 6 on U2B
>>and pin 2 of U2A to ground.  This does two things:  It will bypass
>>any RF getting to the OP-AMP, and slows down the feedback time from
>>the Az-El pots a bit.  When pots get dirty they can cause the relays
>>(if you use them) to chatter or SCR's to trigger needlessly.
>>      When you finish your FodTrack/SatPC32 installation, would you
>>put vital commands and suggested tips for SatPC32/FodTrack on the
>>AMSAT-bb?  This inexpensive, beginner combination includes Doppler
>>correction.  Everyone should use a form of correction eventually
>>while a University CUBESAT station this is now an absolute necessity!
>>      Cliff K7RR

Hi Rick.  Got both of your messages.  First let me comment on the
ferrite beads.  Most anything will do as the bypass capacitors do
most of the job keeping RF out.  ANYTHING will work and if you find
room for two or three on a wire, stack them!  Any surplus store should
be able to help.  AMIDON and PALOMAR are distributors of ferrites.
The rest of the components are very easy to get from JAMECO at
1-800-831-4242.  The LM324 is #192554CJ, LM358 is #23966CJ and the
TLC7528 is # 290087CJ.  The first two are less than $0.50 and the A/D is 
less than three bucks.  Use 2N2222 for the transistors #178511CJ costing
ten for $5. BE SURE and interchange the leads for base and collector!
Start with an ohmmeter and try and find any shorted components first.
Best guess will be the transistors.  Next guess will be the 7528 as
these two chips are connected to the outside world where the lightning
strike would affect them.  FodTrack is dead simple and very inexpensive!
Cliff K7RR
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